The objectives of the first year of the program on Calcium Isotopic Composition in Metabolic Disorders were to design and construct a special purpose high precision mass spectrometer for the determination of isotopic fractionation of calcium ions in biological systems, and to establish in preliminary experiments the range of variability of the 48Ca/40Ca isotope ratio in the mammalian system. This mass spectrometer has been constructed and is undergoing testing for its general performance.